The cytochrome P450 dependent mixed function oxidase system is found in many tissues of vertebrates and is responsible for the metabolism of a variety of therapeutically important drugs among them the tricyclic antidepressants. Recently our laboratory has shown the presence of cytochromes P450 forms b (P450IIB1) and c (P450IA1) using 32P DNA probes in a poly (A)+RNA hybridization assay. The hybridizable bands of both forms are inducible by phenobarbital of beta-napthoflavone, respectively, Furthermore, estrogen and the tricyclic antidepressants amitriptyline and imipramine increase the hybridization of form b. These preliminary data give rise to the hypothesis that brain cytochrome might play a role in antidepressant metabolism in brain and that estrogen levels may influence the expression of cytochromes P450 and in turn antidepressant metabolism. This proposal will test this hypothesis that brain cytochrome might play a role in antidepressant metabolism in brain and that estrogen levels may influence the expression of cytochromes P450 and in turn antidepressant metabolism. This proposal will test this hypothesis by identifying the cytochromes P450 present in brain and localizing them to specific brain areas using 32P labelled DNA or oligonucleotide probes to the various P450 isozymes. We will also characterize the effect of inducers (phenobarbital and beta-napthoflavone), antidepressant substrates (amitriptyline and imipramine), and estrogen on the expression of P450. We will also identify which P450s catalyze antidepressant metabolism in brain using purification and in vitro reconstitution of activity in assay techniques. We will assess the role of estrogen in the expression of brain cytochrome P450 by treating normal and ovarectomized rats with estrogen and other inducers and comparing P450 expression levels. These data will also be used in a correlation of estrogen responsive brain areas with those having estrogen receptors in order to assess how estrogen might exert is regulatory role on brain P450 expression. These studies may aid our understanding of the decreased efficacy of tricyclic antidepressant drugs in the treatment of post menopausal depression and provide a basis for addressing this depression.